Acoustical transducers containing diaphragms are employed to transfer energy between mechanical and electrical states, and such acoustical transducers would include microphones, earphones, beepers (that is, narrow-frequency-band transducers) and loudspeakers, such as, but not limited to, electrodynamic moving-coil and piezoelectric loudspeakers, particularly high-frequency tweeters. A wide variety of material has been suggested for use as diaphragms, both alone and in various laminated and coated forms, in acoustical transducers. Typically, the diaphragm material is shaped into various cone or dome-like forms, alone or in combination, such as, for example, in hyperbolic, exponential and conical-type shapes. Generally, the shape of the diaphragm and the material of the diaphragm provide for the frequency-response characteristics of the diaphragm.
U.S. Pat. No. 4,190,746, issued Feb. 26, 1980, discloses that a wide variety of materials have been employed as diaphragms in moving-coil loudspeakers, to include: metals, ceramics, papers and various plastics in both single-coated and laminate-type forms. The diaphragm material may be laminated or integral with the surround. The patent claims that certain particular plastic materials ar suitable for use over the entire frequency range of a moving-coil loudspeaker, such as polypropylene, polyethylene and ethylene-propylene copolymers as having good damping characteristics and a Young's modulus of about 8.5 to 17.5.times.10.sup.-5 and as particularly suitable materials for wide frequency responses.
Speaker diaphragms have been disclosed which employ carbon fibers as a component of the diaphragm. U.S. Pat. No. 3,930,130, issued Dec. 30, 1975 discloses nonwoven carbonized fiber webs with a high amount of stiffening resin to form a loudspeaker diaphragm. The nonwoven carbon fiber web is formed from chopped carbon fibers using paper making techniques and the web is then impregnated with a hardening resin, such as an epoxy, phenolic or melamine thermosetting resin to form a diaphragm for a loudspeaker. U.S. Pat. No. 4,291,781, issued Sept. 29, 1981 discloses a loudspeaker diaphragm made from a sheet having a wide variety of short fibers including carbon fiber, and which sheet includes short fibers of polyethylene, which are melted during the pressing operation to form the diaphragm cone or dome shape. U.S. Pat. No. 4,410,768, issued Oct. 18, 1983, prepares a composite loudspeaker diaphragm of a foamed resin which contains strengthening fibers such as glass, nylon and carbon fibers.
It is desirable to provide an improved diaphragm material and acoustical transducers, such as moving-coil loudspeakers, made using such diaphragm material which will provide improved frequency response, particularly at high frequencies, and which, while having high Young's modulus values, also are characterized by high internal loss and other desirable acoustical properties.